bus: use EUID over UID and fix unix-creds

Whenever a process performs an action on an object, the kernel uses the
EUID of the process to do permission checks and to apply on any newly
created objects. The UID of a process is only used if someone *ELSE* acts
on the process. That is, the UID of a process defines who owns the
process, the EUID defines what privileges are used by this process when
performing an action.

Process limits, on the other hand, are always applied to the real UID, not
the effective UID. This is, because a process has a user object linked,
which always corresponds to its UID. A process never has a user object
linked for its EUID. Thus, accounting (and limits) is always done on the
real UID.

This commit fixes all sd-bus users to use the EUID when performing
privilege checks and alike. Furthermore, it fixes unix-creds to be parsed
as EUID, not UID (as the kernel always takes the EUID on UDS). Anyone
using UID (eg., to do user-accounting) has to fall back to the EUID as UDS
does not transmit the UID.

1 files changed, 10 insertions, 10 deletions

diff --git a/src/bus-proxyd/proxy.c b/src/bus-proxyd/proxy.c
index 329188ecf8..bd02ee12b3 100644
--- a/src/bus-proxyd/proxy.c
+++ b/src/bus-proxyd/proxy.c
@@ -73,7 +73,7 @@ static int proxy_create_dest(Proxy *p, const char *dest, const char *local_sec,
         if (r < 0)
                 return log_error_errno(r, "Failed to set FD negotiation: %m");
 
-        r = sd_bus_negotiate_creds(b, true, SD_BUS_CREDS_UID|SD_BUS_CREDS_PID|SD_BUS_CREDS_GID|SD_BUS_CREDS_SELINUX_CONTEXT);
+        r = sd_bus_negotiate_creds(b, true, SD_BUS_CREDS_EUID|SD_BUS_CREDS_PID|SD_BUS_CREDS_EGID|SD_BUS_CREDS_SELINUX_CONTEXT);
         if (r < 0)
                 return log_error_errno(r, "Failed to set credential negotiation: %m");
 
@@ -134,7 +134,7 @@ static int proxy_create_local(Proxy *p, int in_fd, int out_fd, bool negotiate_fd
         if (r < 0)
                 return log_error_errno(r, "Failed to set FD negotiation: %m");
 
-        r = sd_bus_negotiate_creds(b, true, SD_BUS_CREDS_UID|SD_BUS_CREDS_PID|SD_BUS_CREDS_GID|SD_BUS_CREDS_SELINUX_CONTEXT);
+        r = sd_bus_negotiate_creds(b, true, SD_BUS_CREDS_EUID|SD_BUS_CREDS_PID|SD_BUS_CREDS_EGID|SD_BUS_CREDS_SELINUX_CONTEXT);
         if (r < 0)
                 return log_error_errno(r, "Failed to set credential negotiation: %m");
 
@@ -433,8 +433,8 @@ static int process_policy_unlocked(sd_bus *from, sd_bus *to, sd_bus_message *m,
                 /* The message came from the kernel, and is sent to our legacy client. */
                 sd_bus_creds_get_well_known_names(&m->creds, &sender_names);
 
-                (void) sd_bus_creds_get_uid(&m->creds, &sender_uid);
-                (void) sd_bus_creds_get_gid(&m->creds, &sender_gid);
+                (void) sd_bus_creds_get_euid(&m->creds, &sender_uid);
+                (void) sd_bus_creds_get_egid(&m->creds, &sender_gid);
 
                 if (sender_uid == UID_INVALID || sender_gid == GID_INVALID) {
                         _cleanup_bus_creds_unref_ sd_bus_creds *sender_creds = NULL;
@@ -446,12 +446,12 @@ static int process_policy_unlocked(sd_bus *from, sd_bus *to, sd_bus_message *m,
                          * case, query the creds of the peer
                          * instead. */
 
-                        r = bus_get_name_creds_kdbus(from, m->sender, SD_BUS_CREDS_UID|SD_BUS_CREDS_GID, true, &sender_creds);
+                        r = bus_get_name_creds_kdbus(from, m->sender, SD_BUS_CREDS_EUID|SD_BUS_CREDS_EGID, true, &sender_creds);
                         if (r < 0)
                                 return handle_policy_error(m, r);
 
-                        (void) sd_bus_creds_get_uid(sender_creds, &sender_uid);
-                        (void) sd_bus_creds_get_gid(sender_creds, &sender_gid);
+                        (void) sd_bus_creds_get_euid(sender_creds, &sender_uid);
+                        (void) sd_bus_creds_get_egid(sender_creds, &sender_gid);
                 }
 
                 /* First check whether the sender can send the message to our name */
@@ -483,7 +483,7 @@ static int process_policy_unlocked(sd_bus *from, sd_bus *to, sd_bus_message *m,
                 if (m->destination) {
                         r = bus_get_name_creds_kdbus(to, m->destination,
                                                      SD_BUS_CREDS_WELL_KNOWN_NAMES|SD_BUS_CREDS_UNIQUE_NAME|
-                                                     SD_BUS_CREDS_UID|SD_BUS_CREDS_GID|SD_BUS_CREDS_PID,
+                                                     SD_BUS_CREDS_EUID|SD_BUS_CREDS_EGID|SD_BUS_CREDS_PID,
                                                      true, &destination_creds);
                         if (r < 0)
                                 return handle_policy_error(m, r);
@@ -494,8 +494,8 @@ static int process_policy_unlocked(sd_bus *from, sd_bus *to, sd_bus_message *m,
 
                         sd_bus_creds_get_well_known_names(destination_creds, &destination_names);
 
-                        (void) sd_bus_creds_get_uid(destination_creds, &destination_uid);
-                        (void) sd_bus_creds_get_gid(destination_creds, &destination_gid);
+                        (void) sd_bus_creds_get_euid(destination_creds, &destination_uid);
+                        (void) sd_bus_creds_get_egid(destination_creds, &destination_gid);
                 }
 
                 /* First check if we (the sender) can send to this name */